The WISE family comets

In the little over one year that the Wide-field Infrared Survey Explorer (WISE) spacecraft surveyed the sky, it captured images of hundreds of millions of objects. Many of these were previously known stars, galaxies, and the like, but it also added a few newcomers to our catalogs, including a score of comets:

[Click to encomanate.]

Why did WISE find them, and not ground-based observers? Lots of reasons come to mind. Comets are not really the spectacular and brilliant objects commonly thought; at least, not all of them are. The solid part of a comet is usually a mix of rock and ice, the ice being made of water, ammonia, carbon dioxide, and other materials we tend to think of as gases here on Earth. But in the depths of space, where it’s cold, they can remain frozen solid… until the comet nears the Sun. Then, the materials go from a solid directly to a gas, surround the solid nucleus, and reflect a whole lot more sunlight. The comet gets bright and can be spotted more easily.

Even then, it may not be easy. The comet may be small ...

Full story at http://blogs.discovermagazine.com/badastronomy/2011/06/03/the-wise-family-comets/